1. Field of the Invention
The present invention relates to a molded glass lens, a mold assembly, a method for manufacturing a mold assembly and a method for manufacturing a molded glass lens, and more particularly to an axially symmetrical molded glass lens, a mold assembly for an axially symmetrical molded glass lens, a method for manufacturing a mold assembly for an axially symmetrical molded glass lens and a method for manufacturing an axially symmetrical molded glass lens.
2. Description of Related Art
Lenses are core elements of optical devices such as microscopes, magnifier telescopes, digital cameras and video cameras, are manufactured in a mold with lens surfaces cut with a computer numerical control (CNC) grinding machine and are high precision.
With reference to FIG. 1, most conventional hot-press molded lenses (110) provide clear and sharp images, are made of glass and are circular, and each hot-press molded lens (110) has a central, axially symmetrical lens, a mounting flange and an annular intermediate area. In telescopes and microscopes with the primary function of magnifying images, the lens quality greatly affects the precision of the magnifying power and focal length.
The mounting flange is formed on and protrudes radially out from the axially symmetrical lens, is used to mount the hot-press molded lens (110) in an optical device and has a flat upper surface and a flat lower surface. The flat upper surface has an inner edge. The flat lower surface has an inner edge and is parallel to the flat upper surface.
The annular intermediate area is formed of the flat upper and lower surfaces respectively and may be a sharp edge and often has optical discontinuities. The discontinuities cause aberrations that adversely affect images at or near the edge of the axially symmetrical lens.
A conventional mold for manufacturing a hot-press molded lens (110) comprises two molds (100). The molds (100) mate with each other to form an internal cavity in which a hot-press molded lens (110) is pressed. Each mold (100) has an intermediate area, an axially symmetrical lens transferring area (101) and a flat area (102).
The axially symmetrical lens transferring area (101) is formed in or on the flat surface of one mold (100), may correspond to an axially symmetrical lens transferring area (101) in or on the inner surface of the matching mold (100) and has a sharp edge (103). The sharp edge (103) is formed around the axial lens transferring area (101) at the inner surface.
A conventional method of manufacturing the mold for a glass lens comprises lathing or grinding a piece of mold with a lathe cutting tool or a grinding tool. The axially symmetrical lens transferring area (101) is circular and axially symmetric, is formed in or on the inner surface of the mold and forms an outer surface on the glass to form the molded glass lens when the molten glass is in the mold.
A conventional lathing or grinding process to form a mold for a glass lens from a piece of mold is implemented with a computer numerical control (CNC) lathe or grinder. The CNC lathe or grinder rotates a piece of mold, cuts a desired shape in the piece of mold and has a cutting tool or grinding tool and a computer. The computer controls the cutting tool or grinding tool to cut a specific shape in the piece of mold and has a cutting-path formula as follows.
  Z  =                    CY        2                    1        +                              1            -                                          (                                  1                  +                  K                                )                            ⁢                              C                2                            ⁢                              Y                2                                                          +                  A        2            ⁢              Y        2              +                  A        4            ⁢              Y        4              +    …    +                  A                  2          ⁢          n                    ⁢              Y                  2          ⁢          n                    
wherein “Z” is a vertical coordinate, “Y” is a horizontal coordinate and “A2,” “A4,” “A2n,” “C” and “K” are constants that can be adjusted.
However, the axially symmetrical lens transferring area (101) connects to the flat area (102) on the mold (100) and forms the sharp edge (103) between the axially symmetrical lens transferring area (101) and the flat area (102). Molten glass material is poured into the mold between the flat area (102) and the axially symmetrical lens transferring area (101). However, the molten glass rubs against and breaks the sharp edge (103) when passing through the sharp edge (103), which decreases quality, precision and production rate of the axially symmetrical lens.
Japan patent No. 1188437 discloses a mold for manufacturing a molded glass lens, which has an axially symmetrical lens transferring area, a flat area and an intermediate area. The intermediate area is formed on the mold between the axially symmetrical lens transferring area and the flat area, is annular and curved and has a constant radius of curvature preferably larger than 0.2 millimeter. When a glass lens is molded, molten glass flows smoothly over the intermediate area without causing aberrations in the glass or damaging the mold. The resultant glass lens has no undesired discontinuities because no sharp edge exists on or between the axially symmetrical lens transferring area and the flat area on the mold (100).
However, a method for manufacturing the mold described in the Japan patent comprises two distinct cutting steps instead of one. The cutting steps respectively cut the axially symmetrical lens transferring area (101) and an intermediate area in the mold (100). Furthermore, the steps are implemented with two different cutting-path formulas corresponding respectively to the axially symmetrical lens transferring area and intermediate area. However, two cutting-path corrections cannot be made simultaneously to the two different cutting-path formulas in CNC lathe machines currently available. Therefore, manufacturers must change the cutting-path formulas for each mold (100) or sequentially cut multiple molds (100) with one cutting-path formula. Therefore, the mold has a low production rate, and the mold quality is questionable, at best.
Japan patent publication No. 2000-249812 discloses an optical glass lens, a mold and a method for manufacturing the mold. The mold has an axially symmetrical lens transferring area, a flat area and an intermediate area. The intermediate area is between the axially symmetrical lens transferring area and flat area and is curved. However, the method for manufacturing the mold also has two steps respectively with different cutting-path formulas applicable respectively to the axially symmetrical lens transferring area (101) and the intermediate area. The transferring area and intermediate area still have to be corrected sequentially. Therefore, the mold still has insufficient precision and a low production rate.
A conventional method for manufacturing a glass lens is to put glass into a mold to form the glass lens.
To overcome the shortcomings, the present invention provides an axially symmetrical molded glass lens, a mold assembly for an axially symmetrical molded glass lens, a method for manufacturing a mold assembly for an axially symmetrical molded glass lens and a method for manufacturing an axially symmetrical molded glass lens to mitigate or obviate the aforementioned problems.